Remove an outdated comment from `kernel/constr.ml`
Remove an outdated comment from `kernel/constr.ml`

It was forgotten in bc26ad1cbbeb0a8aa2ac36916db3c09330bacfd0, as per https://coq.zulipchat.com/#narrow/stream/237656-Coq-devs-.26-plugin-devs/topic/Confusing.20comment.20in.20the.20kernel/near/304760859
Zimmi48/coq,coq/coq,SkySkimmer/coq,coq/coq,SkySkimmer/coq,SkySkimmer/coq,Zimmi48/coq,Zimmi48/coq,Zimmi48/coq,ejgallego/coq,ejgallego/coq,coq/coq,coq/coq,ejgallego/coq,ejgallego/coq,SkySkimmer/coq